https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67839
Bug ID: 67839 Summary: Bit addressable instructions generated for invalid memory address Product: gcc Version: 6.0 Status: UNCONFIRMED Severity: major Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: senthil_kumar.selvaraj at atmel dot com Target Milestone: --- Bit addressable instructions (sbi, cbi, sbis, sbic) only work on IO addresses 0x0-0x1f (inclusive). The compiler generates these instructions for IO address 0x20 as well. The problem is in the specification of low_io_address_operand predicate, which has (define_special_predicate "low_io_address_operand" (ior (and (match_code "const_int") (match_test "IN_RANGE (INTVAL (op) - avr_arch->sfr_offset, 0, 0x20 - GET_MODE_SIZE (mode))")) (and (match_code "symbol_ref") (match_test "SYMBOL_REF_FLAGS (op) & SYMBOL_FLAG_IO_LOW")))) While this looks ok, gcc invokes low_io_address_operand with mode set to VOID, and GET_MODE_SIZE for VOID returns 0, so the effective range becomes 0x0-0x20. gcc does pass the correct mode if the operand mode is set in the define_insn that uses this predicate. Don't know why it isn't set, and why define_special_predicate is used instead of define_predicate. Note that io_address_operand predicate has a GET_MODE_SIZE call as well, so the range check is off by one in it too